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How big a propeller would I need to turn a 3500 watt AC gererator? Answered

A friend of mine gave me a 3500 watt gasoline AC generator because he burnt the engine and he did not want to fix it due to cost. I want to use a propeller instead of a gas engine to make it operational. Is this practical? The wind here blows constantly between 20 and 30 mph.

3 Replies

Your alternator will have to turn at 3600 RPM for Two pole or 1800 for 4 pole.
Most alternators are Two pole and must turn at this speed only to output
60 Hertz. ac.and to have the voltage at the correct value 120 volts-230.
a wind mill can not run at a steady speed you could probably use a gearbox to
up the RPM which would make some output though the frequency would be
erratic and no appliance would function. You would have to use diodes to
convert to to DC current then charge a Battery Bank to make it useful . A low voltage alternator (24 volt . from a Semi Truck Tractor would be more suitable
for a DC System. It would Take a Big one.

There is a limit of 900mm dia for wind turbines in Australia. A 900mm turbine can generate 3kw under ideal conditions with wind speeds of 30mph but this only occurs on very rare occasions in most areas. But the generator has to be designed to generate the output at the speed of rotation of the blades. That's why the generator has to be designed for application. There's a lot more to it than just hitching up a generator to a set of blades.

Did you remove the engine part? Forcing cylinders up and down would need somewhere around 100-150 mph wind. If you remove the engine, see how much torque is needed to spin the shaft. In addition, the shaft will be harder to spin under a load. Try looking up wind powered generators and see if you can get the blade area and size from them. I know that buying extra carbon blades for these devices can cost around $100 a blade. I am assuming you aren't planning to run this at full 3500 watt load.